valve. The pattern here will be of the same shape as the finished
casting, excepting the square holes in the centre, which we will
suppose to be cast in, to be afterwards dressed up with a rough
file. Square core prints of any convenient length are put on either
side of the boxes, and of a diameter equal to the hole to be cast,
allowing a small amount for cleaning up (see pattern, Fig. 7).
A core box is now to be made, which is shown in Fig. 8, and
consists of two blocks of wood, hollowed out in such a way as to
represent the square hole required, and of a length equal to that
across the core prints from end to end The pattern is next
placed in the sand, as drawn in Fig. 9, and parting made, then
rammed up, with gate at fe, and vents here and there. Core sand
mixed with water is put in the core box (which fits together by
means of the pegs PP), smoothed off, removed, and placed in the
core stove to dry. The mould is finished and blackened, and
the core treated with black wash, which is charcoal dust mixed
with clay water, and used for the same purpose as blackening.
The core being put in place, as shown in Fig. 9, everything is
ready for the reception of the metal.
We shall now take the moulding of a Chain Pulley, by a
very ingenious method. Fig. 10 represents the pattern, with core